Currently, absorbance measurement methods are applied to analyses of various components. Component analysis by such an absorbance measurement method is carried out in accordance with the following procedures, for example. First, a transparent container (cell) containing a specimen mixed with a pigment is irradiated with light having a wavelength corresponding to the pigment, from a light source such as a halogen lamp or LED. Next, the intensity I of the transmitted light that has passed through the transparent container and the specimen is measured with a light-receiving element.
Later, the absorbance (=log10(I0/I)) is calculated from the measured intensity I of the transmitted light and a blank value I0 that has been measured in advance. Thereby, the component amount of the material labeled by a pigment can be detected (see Patent Document 1, for example). The blank value I0 is measured by irradiating a water-containing or empty cell with light from the light source. The absorbance measurement method is not limited to the above-mentioned transmission type utilizing transmitted light, but a reflection type using light reflected by a measurement target is known as well.
The absorbance measurement method is used also for measuring a blood glucose level in a blood. A blood glucose meter for measuring a blood glucose level by the absorbance measurement method is called generally a colorimetric blood glucose meter. For decreasing the size, a colorimetric blood glucose meter developed to be carried by a patient includes not a transparent container but a disposable sensor or chip made of a nonwoven fabric or the like.
The sensor or chip is impregnated with a reagent that develops color as a result of a reaction with glucose in the blood. Since the transmitted light quantity of light passed through the sensor or chip varies depending on the color development level, the blood glucose level can be obtained from the measured absorbance. In such a portable colorimetric blood glucose meter, measurement of the blank value is carried out without attaching a sensor or a chip.    Patent document 1: JP 2001-91518 A